1. Field of the Invention
The present imeion is directed to a chemical complex which serves as a "loss of dry" inhibitor, particularly in an oil-based paint, and as a cure accelerator having gel-time stabilizer and color development inhibitor characteristics in polyester resin polymerization. This invention especially relates to the preparation of a complex reaction product of an oil soluble cobalt soap and an oil soluble overbased calcium soap.
2. Description of Related Art
Oil based paints generally reremetal soaps (metal salts of long chain organic acids), particularly a cobalt soap such as cobalt naphtheate, in combination with a lead soap or a zirconium soap, to catalyze the polymerization of drying oils and other oxidizable vehicles used in such coating compositions. While the metal soaps perform quite effectively when they are first compounded in such coating compositions, these compositions often exhibit a reduction in drying rate on aging. For example, when an alkyd paint is highly pigmented, a phenomenon often occrs which has been called "loss of dry"--that is, the alkyd paint does not dry as rapidly after prolonged storage as when first prepared. For example, a paint which may dry in 4 hours when first prepared, may require 6 to 8 hours or longer for drying after 30 days of storage.
It has been suggested that the reduction in the drying rate results from an adsorption of the metal soaps on the surface of pigment particles and extenders used in the coating composition, or possibly by a reacon between the metal soaps and other coating constituents that produce insoluble, and inactive metal compounds. Whatever the reason, the reduction in the drying rate of such coating compositions is generally considered a disadvantage.
Certain "loss of dry" inhibitors have been available in the prior art, which function to counteract the loss of activity observed when using the conventional metal soaps. U.S. Pat. No. 3,901,837, for eaample, describes a solution of a mixture of cobalt, calcium and zinc, or zirconium, oil-soluble metal salts (soaps) of branched-chain aliphatic monocarboxylic acids, having 6-14 carbon atoms, as a loss-of-dry inhibitor. Particularly preferred is a metal salt solution of cobalt 2-ethylhexoate or cobalt isononanoate, calcium naphihenate and zinc 2-ethylhexoate. One loss-of-dry inhibitor comprises a solution of these soaps in an inert non-polar organic solvent. The soaps can be prepared by reacting the oxides or hydroxides of the metals with the appropriate organic acids directly in an organic solvent or by precipitation of the soaps by heating aqueous solution ofthe sodium salts of the acids with water-soluble salts of the metals.
U.S. Pat. No. 4,032,354 describes a loss-of-dry inhibitor constituting a combination of oil-soluble and oil-insoluble calcium salts; in particular a suspension of finely divided calcium hydroxide in a solution of a calcium salt of a 6-14 carbon atom branch-chain aliphatic or 6-10 carbon atom cycloaliphatic monocarboxylic acid or mixture of such acids. Particularly preferred is an organic solvent solution of calcium naphtenate with suspended calcium hydroxide. The loss-of-dry inhibitor composition can be prepared by heating a suspension of a stoichiometric excess of finely-divided calcium hydroxide in an inert solvent with one of the noted organic acids.
"Basic" cobalt naphthenate, which according to the known art consists essentially of cobalt hydroxide dispersed in a carrier such as a petroleum oil and a liquid cobalt naphthenate soap solution also has been used as a loss of dry inhibitor in oil-based coating compositions. "Basic" cobalt naphthenate has been observed to cause wrinkling in paint films when used at efficacious concentrations and causes undesired staining in white and light-colored coatings.
Unfortunately, preparing compositions, such as the "basic" calcium naphthenate of U.S. Pat. No. 4,032,354, "basic" cobalt naphthenate or similar compositions, in a form suitable for use in coating applications has proven to be quite difficult, requiring special milling or grinding equipment to disperse the metal hydroxide adequately. The heat of the milling operation also tends to oxidize the product and discolor it, obviously an undesired consequence in coating applications. Furthermore, it has been difficult to suspend the metal hydroxide satisfaorily in the product, which must remain sufficiently fluid so that it can be poured from a drum.
Compositions prepared by milling calcium or cobalt hydroxide are not completely soluble in vehicles such as petroleum solvent, drying oils or resin solutions. Usually, when added to such vehicles and allowed to stand before use, a certain amount ofthe metal oxide or hydroxide (calcium hydroxide, and cobalt hydroxide (or cobalt oxide)) will be found to have settled out. Besides contributing to a lengthening of the drying time, the presence of this insoluble loss of dry inhibitor component may also cause hazing of clear films of paint or the hazing of a polyester resin.
As a result, there remains a need in the art for a loss of dry inhibitor which better maintains drying activity during storage, is easier to use in coating compositions, and avoids subsidiary problems such as settling out or hazing.
Unsaturated polyester resin compositions also employ metal soaps, akin to those discussed above, as cure accelerator systems. Such resins typically comprise solutions of an unsaturated polyester resin in a polymerizable monomer which cros-links the polyester polymer chains. The polyester resin and monomer copolymerize upon the introduction of a peroxide initiator to form a rigid, insoluble, infusible material. These unsaturated polyester resin compositions have found widespread use in the production of coatings, laminates, cast articles, molded articles, and other shaped articles.
The cure accelerator is usually added to an unsaturated polyester resin composition to accelerate the decomposition of the peroxide catalyst to free radicals and thereby intite or speed the curing of the composition (gel formation and ultimate hardening) at relatively low temperatures, i.e., at temperatures generally in the range of 0.degree. to 30.degree. C. Cobalt soaps of organic acids remain one of the most widely-used cure accelerators for the low temperature decomposition of peroxide catalysts and the curing of unsaturated polyester resin compositions.
It also is known that the curing time of unsaturated polyester resin compositions at low temperatures can be further reduced by the use of a second accelerator in combination with the normally used cobalt compounds. Such co-accelerators include amines, such as dimethylaniline, diethylethanolamine and tetramethylbutane diamine and aliphatic polyamines, such as diethylene triamine and 3,4-diamino-3,4-dimethylhexane.
U.S. Pat. No. 4,175,064 describes another accelerator system for peroxide-initiated unsarated polyester resin compositions. The accelerator system comprises a mixture of neutral cobalt and potassium salts (soaps) of organic monocarboxyic acids having from 6 to 24 carbon atoms.